ABSTRACT Many people know the general story about RSA and large (probably) prime numbers, without having an idea of how to perform arithmetic operations with the numbers of thousands of bits. Even if they want to develop their own tool for a digital signature, they give up because they think that special hardware-software offers are required for that. In this paper we want to show that even by using a very simple console application, the tools for signature can be developed. Those tools are not as powerful and functional as the products of renowned companies, but they are sufficient to stimulate the interest in cryptography (and the coding of known algorithms is the best way for that), and that is our overriding and permanent goal[3].